As a result of its structure and modes of processing sensory input, the nervous system is selectively sensitive to complex properties and combinations of sensory stimulation. Current research of this laboratory is concerned with three aspects of this processing. (1) The development of meridional differences in the visual acuity of infants and young children. We are using two methods during the first few years of life: (a) the looking preference in infants, and (b) the visually evoked potential, produced by counterphased gratings, which is applicable to all ages. In addition to working with normal (emmetropic) subjects, we are also studying congenital astigmats in order to check on the hypothesis that continued exposure to blurred edges causes optically uncorrectable loss of acuity. If the infant astigmat shows normal meridional variation in acuity, as our evidence suggests, then it is likely that the large variations shown in astigmatic adults must occur as a result of exposure during the first few years of life. We seek to define the timing and course of this modifiable period. (2) The properties of color and edge sensitive channels. These channels are monocular but converge on binocular analyzers; they are orientation and spatial frequency selective. Using the adaptation-aftereffect paradigm, we seek to confirm and to explore the mechanism of the anomalous finding that the visual system is increasingly sensitive, at suprathreshold levels, to colored gratings of increasingly high frequency. (3) The interaction among visual, vestibular, and proprioceptive stimuli determining spatial orientation. Moving visual fields simulate the effects of inertial forces acting on the labyrinth. By measuring the subjective vertical as well as torsional eye movements during real tilt, visually simulated tilt, and stimulation of muscle receptors, we are studying the interaction among these determinants of posture and coordinated movements in space.